Current engine emissions regulations place significant challenges to the ability for an engine to quickly react to sudden changes in load demand. In order to avoid large particulate emissions, the engine must change operating modes to a significantly higher level of fuel consumption during transient load events in order to meet emissions requirements. This limits the rate at which an engine can respond to the load transient which translates into lower performance for the operator. It would be desirable to have a vehicle drive system which complies with emission regulations and which permits an engine to respond rapidly to changes in load.